Does anyone know what the most die hard, longest lasting synth ever made is?
Hammond Tonewheel Organ (additive synthesizer). Hands down winner.
Bummer, it had to be an organ..
Built from 1935 to 1974. Thousands still in use. gonna be pretty hard to beat.
DX-7 would be a tough one to beat in the electronic arena. supposedly 160,000 of them made.(Hammonds are Electro-mechanical)
And I guess there would be an argument that pipe organs would be the oldest, longest lasting emulators.
I can appreciate that. Never got into the organ sound though.
I’d have to go with pipe organs as well, Just Me. But as far as ELECTRONIC instruments go, not counting electro-mechanical, I’d have to say Moog modulars are the longest lived electronic instruments. Some of them are 40 years old already, and still going strong. 
Id say that the Theremin is a contender.
It depends on what you mean by Synth. I mean the Theremin is essentially an osc, older than the hamond, and has very limited waveshaing capabillity. Accurately synthesized sounds in various registers from violins to voices.
Longest lasting perhaps, but not as widely in use as the Hammond.
EricK
I was thinking more along the lines of synths like Kurzweil, Korg, Moog, Alesis, Yamaha, but not limited to those.
Just the most durable keyboard synth.
Durable? CZ101. Can’t hurt them.
Prolific? DX7 family
Built like tanks? Early ARP.
Best all around synth “I” ever owned. Toss up between Arp 2600 and Ensoniq SQ-80.
The most durable? The DX-7 is pretty durable. Organs are also durable, particularly Hammonds. I’d say Minimoogs are also very durable.
I believe the first subtractive synth was the Hammond Novachord. If what I read on some websites is accurate, there are some left that are still working, though I believe many, if not all of them, were restored at some point.
What about the Telharmonium that predates the hammond stuff? Is it in the Smithsonian somwwhere or still working???
Sadly, I believe the only Telharmoniums left are either photos, drawings, or technical diagrams. 
I would REALLY love to be proved wrong on this, though. I would also love one for myself, and will have one built if I ever win the lottery. The ultimate steam punk synthesizer, even if it WAS additive. 
Interesting article:
http://www.discretesynthesizers.com/archives/miessner/em1936.htm
Awesome find! 
Because the Telharmonium predated the electron tube there was no technology at the time to amplify signals to audible levels. The method of generating tones created so much interference in neighboring phone line networks that it was a nuisance. That’s why the system was so huge and bulky. Plus it took several railroad boxcars to transport the thing. Thus at the end of its life it was a white elephant especially with the dawn of tube amplifiers which were a hundred times more compact. Not only was it dismantled but most of the precious metals either were recycled or went into the war effort.
church-organ
human mouthsynth
ems synthi
From what I’ve heard, the Korg MS-20 is easy to service and is mostly discrete, so finding parts shouldn’t be too difficult.
MY Woodstock era Moog just turned 40 years old!
It gets played daily. First thing I turn on when I get home from work.
Still one of my favorite sounding synthesizers.
910 build date August 1969!
Sweet. Got any other pictures of it?